1. Field of the Invention
The present invention relates to a method of receiving light and a light receiving module of less polarized light dependency. The light receiving module is used for evaluating the polarization characteristic of various optical components.
2. Description of the Related Art
The arrangement of a conventional light receiving module will be described hereinafter with reference to FIG. 8. In FIG. 8, denoted at 2 is a light receiving element and 1A is incident light to the light receiving surface of the light receiving element 2. The light receiving element 2 converts the incident light 1A into an electric signal to measure the output of the incident light 1A.
In FIG. 8, the light receiving surface 2A of the light receiving element 2 receives the incident light 1A with the normal of the light receiving surface 2A tilted by several degrees relative to the optical axis of the incident light 1A. When light reflected by the light receiving surface 2A returns to the light source, for example in case of laser, it deteriorates the performance of the light source to obstruct accurate measurement of light. Such a method of preventing a light receiving element from being deteriorated in performance by tilting the same is, for example, disclosed in Japanese Patent Publication No. 54-181.
In FIG. 8, even if the incident light 1A is unchanged in light output, the polarized state of the incident light 1A or the variation of wavelength thereof cannot be neglected for high-accuracy measurement. In FIG. 8, tilting the normal Of the light receiving element 2 relative to the optical axis of the incident light 1A causes difference in index of refraction depending on the polarized state of the incident light 1A and consequently in amount of passing light at the light receiving surface 2A of the light receiving element 2. The amount of passing light referred to here is the amount of light obtained by subtracting that of reflected light from that of the whole incident light 1A.
FIG. 9 shows a relationship between the light output received by the light receiving element 2 and the angle of rotation of the light receiving surface 2A about the optical axis of the incident light 1A in case the normal of the light receiving surface 2A of the light receiving element 2 is tilted relative to the optical axis of the incident light 1A. The incident light 1A referred to here is polarized linearly. The axis of ordinate represents light output received by the light receiving element 2 and that of abscissa represents the angle of rotation of plane of polarization. When the normal of the light receiving surface 2A is tilted by 4.degree. relative to the optical axis in FIG. 9, polarized light dependency, described later, is about 0.006 dB.
As illustrated in FIG. 9, there is a problem in that the light output finally detected by the light receiving element 2 varies with the variation of polarized state even if the amount of the incident light 1A is constant in light output. This variation of light received by the light receiving element 2 will be called hereinafter as polarized light dependency.